The frequency and type of ventricular ectopic activity in populations with various degrees of coronary heart disease (CHD) will be determined. Prolonged ambulatory electrocardiographic monitoring as well as isometric and sub-maximal bicycle and treadmill exercise will be employed in patients with previous myocardial infarctions or angina pectoris as well as in control patients free of clinical manifestations of CHD. Specific objectives include: 1. Characterization of the trend of ventricular premature beats (VPB) detected by periodic monitoring during the first year after a myocardial infarction. 2. Comparison of the type and specificity of the various arrhythmias provoked during and following isometric and dynamic exercise to the arrhythmias detected during prolonged ambulatory monitoring in patients with previous infarctions and in controls. 3. Correlation of the arrhythmias detected during monitoring and provoked by exercise to the extent of coronary artery pathology as determined by angiographic and biochemical studies in patients with coronary heart disease. And, to assess any post- operative change in ventricular arrhythmias in those patients undergoing myocardial revascularization surgery. 4. Comparison of the efficiency of VPB detection by the semi-automated Holter-Avionics and American Optical systems, and a fully automated special purpose digital computer, and to develop improved methods for arrhythmia data acquisition and reduction.